1. Field of the Invention
An aspect of the present invention relates to a trellis encoder and a trellis encoding device having the same. More particularly, the present invention relates a trellis encoder and a trellis encoding device having the same, which performs initialization of a supplementary reference signal (SRS) before encoding the SRS in a digital broadcast transmitter for transmitting a transport stream into which the SRS has been inserted.
2. Description of the Related Art
With the development of electronic and communication technologies, digital technologies have been introduced into the field of broadcasting system, and diverse standards for the digital broadcasting have been published. One of such standards is an Advanced Television Systems Committee (ATSC) Vestigial Sideband (VSB) system that is an American-type digital terrestrial broadcasting system. The ATSC VSB system is a signal carrier type broadcasting system, and uses a field sync signal in the unit of 312 segments.
FIG. 1 is a block diagram illustrating the construction of a transmitter/receiver of an ATSC DTV standard as a general American-type digital terrestrial broadcasting system. Referring to FIG. 1, the digital broadcast transmitter includes a randomizer 11, a Reed-Solomon (RS) encoder 12, an interleaver 13, a trellis encoder 14, a multiplexer (MUX) 15, and a modulator 16.
The randomizer 11 randomizes a transport stream. The RS encoder 12 performs an RS encoding that adds RS parity bytes to the randomized transport stream in order to correct bit errors occurring due to the channel characteristic in a transport process. The interleaver 13 interleaves the RS-encoded data according to a specified pattern. The trellis encoder 14 performs a trellis encoding of the interleaved RS-encoded data at the rate of ⅔ and then performs mapping of the trellis-encoded data onto 8-level symbols. The MUX 15 inserts a field sync and a segment sync into the transport stream outputted from the trellis encoder 14. The modulator 16 inserts a pilot tone into an output signal of the MUX 15 by adding a DC value into the output signal of the MUX 15, performs VSB modulation of the output signal, and then performs up-conversion of the modulated signal into an RF channel signal to transmit the converted signal through a channel.
The modulated signal transmitted from the digital broadcast transmitter is inputted to a receiver through the channel. A digital broadcast receiver as illustrated in FIG. 1 includes a demodulator 21, an equalizer 22, a Viterbi decoder 23, a deinterleaver 24, an RS decoder 25, and a derandomizer 26. The demodulator 21 performs a sync detection and demodulation of the received signal. The equalizer 22 compensates for a channel distortion of the demodulated signal. The Viterbi decoder 23 corrects errors of the equalized signal and decodes the equalized signal to symbol data. The deinterleaver 24 rearranges the data dispersed by the interleaver 13 of the digital broadcast transmitter. The RS decoder 25 corrects errors according to parities. The derandomizer 26 derandomizes the data corrected through the RS decoder 25 and outputs an MPEG-2 transport stream. The digital broadcast transmission/reception is performed in the above-described manner.
FIG. 2 illustrates a VSB data frame for use in the American type digital broadcasting (8-VSB) system. As shown in FIG. 2, one frame is composed of two fields. One field is composed of one field sync segment that is the first segment, and 312 data segments. Also, one segment in the VSB data frame corresponds to one MPEG-2 packet, and is composed of a segment sync signal of four symbols and 828 data symbols.
In FIG. 2, the segment sync signal and the field sync signal are used for the synchronization and equalization in the digital broadcast receiver. That is, the field sync signal and the segment sync signal refer to known data between the digital broadcast transmitter and receiver, which is used as a reference signal when the equalization is performed in the receiver side.
On the other hand, in order to improve the performance of receiving turbo streams, a technique of inserting a supplementary reference signal (SRS) into a dual transport stream has been developed. Accordingly, it is required to provide a technique for properly encoding the dual transport stream into which the SRS has been inserted. In this case, since the value of the SRS may differ according to values pre-stored in memories provided in the trellis encoder 14, it is necessary to provide a method of properly resetting the memories in the trellis encoder 14 after processing the SRS. In addition, if the memory is compulsorily set to “0” in a memory resetting process, a value outputted by the mapper of the trellis encoder 14 may have a DC offset. Accordingly, a need exists for a method for solving the above-described problems.